Re-expansion gas turbine engine with power transfer between turbines



March 1966 E. E. FLANIGAN ETAL 3,237,404

RE-EXPANSION GAS TURBINE ENGINE WITH POWER TRANSFER BETWEEN TURBINESOriginal Filed March 7, 1962 4 Sheets-Sheet 1 FUEL c IO SUMP SPEEDTRANSDU SPEED SDUCER (OPTIONAL) TORQU SENSOR POWER SFER CLUTCHAUXILIARIES CLUTCH OVER- TE MRERATURE VALVE 10 sump ACCELERATION VALVESUP TORQUE PROGRAMMER TEMPERATURE COMRENSATOR VALVE TO SUIVIP ATTORNEYMarch 1, 1966 E. E. FLANIGAN ETAL 3,237,404

FIE-EXPANSION GAS TURBINE ENGINE WITH POWER TRANSFER BETWEEN TURBINESOriginal Filed March 7, 1962 4 Sheets-Sheet 2 [2:2 I}, 1/ J7 V j; /L L F7 /4 w fi AV 1/ 1/ in; 1/ W 75 l i/ a .Z/ A? If i 76' \\r l/ u 7/ 25% Ha (a 7/ 7i a W TTORNEY March 1, 1956 E. E. FLANIGAN ETAL 3,237,404

REX-EXPANSION GAS TURBINE ENGINE WITH POWER TRANSFER BETWEEN TURBINESOriginal Filed March 7, 1962 4 Sheets-Sheet 5 SUMP % INVEN TORS March 1,1966 E. E.

BET-EXPANSION GAS TURBINE ENGINE WITH FLANIGAN ETAL POWER TRANSFERBETWEEN TURBINES Orlgmal Filed March 7, 1962 4 Sheets-Sheet 4 jzaf/POWER TRANSFER CLUTCH LOCKED UP OUTPUT SHAFT SPEED- PERCENT www Z TEMPWITH M O O O mI aIimj OFQEDWZOU E2 UEUMQW I nn IEJZE mZmEE 0 550a 20E399 ow 0 o o 0 IO 8 6 5 3m DI .I w E 6 o m 9 6 w T w m m 0 F 00 MM 8 2T j 8 m o m M E p 6 7 m OM n m E D1 8 S O R w 6 9 m RTE/1m 10E 0 A 55020 20E 8 m. QEQEFVQ 550E N E m G M w i U FL E P s m N R E N E G S A GPERCENT AMPLIFIER d I m w w N A /f W W ah ELECTRIC United States Patent3,237,404 RID-EXPANSION GAS TURBINE ENGINE WITH POWER TRANSFER BETWEENTURBINES Eugene E. Flanigan, Bloomfield Hills, and Robert W. Guernsey,Rochester, Mich., Jerry R. Roan, Plainfield, Ind., and Richard M. Zeelr,Utica, Mich., assignors to General Motors Corporation, Detroit, Mich., acorporation of Delaware Continuation of application Ser. No. 178,121,Mar. 7, 1962. This application May 3, 1965, Ser. No. 456,031 22 Claims.(Cl. 6039.16)

This application is a continuation of our application Serial No.178,121, filed March 7, 1962.

Our invention pertains to gas turbine engines. It is particularlydirected to improving the efiiciency of engines of a gas-coupled or freeturbine type; that is, engines which have two or more independentlyrotatable turbines. This is a preferred type of gas turbine for manyapplications such as propulsion of automobiles, trucks, boats, andaircraft. An engine of the free tur bine type includes a compressor,combustion apparatus, and a turbine driving the compressor, theseconstituting a gas generator or gasifierv The gas generator may have twospools or compressor-turbine combinations. The engine also has a poweror load turbine energized by the hot gases from the gas generator whichdrives an external load.

One great advantage of free turbine engines is flexibility, since thespeed of the output shaft may vary widely without affecting theoperation of the gas generator. The power output of the engine may bevaried by chang ing the fuel supply to vary the gas energy delivered tothe power turbine, but variations in speed of the power turbine toaccommodate the load are not followed by the gas generator, which mayoperate at an efiicient speed. The power turbine may even be stalled,and thus may be coupled directly to the driving wheels of a vehicle. Forsuch service, this is a desirable characteristic.

Engines of the free turbine type share with single shaft turbines oneimportant handicappoor fuel economy at light load. The specific fuelconsumption of a regenerative gas turbine is no higher than dieselengines or gasoline engines at full load. However, in light motorvehicles, the output of the engine is likely to be less than half fullpower most of the time. High fuel consumption under these conditionsgreatly increases the overall fuel cost.

This invention is directed to improving the specific fuel consumption ofthe engine under part-load conditions by extracting power from the gasgenerator turbine and delivering it to the load. Thus, to an extent, thegas generator turbine is teamed with or parallel with the power turbine.By suitable control of such transfer of power, sensational improvementsin part-load fuel economy can be had. For example, starting with aregenerative engine having a full load BSFC of 0.44, a half-load BSFC of0.52, and quarter-load BSFC of 0.62; adding power transfer according tothis invention to the engine, the full load BSFC remains as before buthalf-load BSFC is slightly under 0.44, and quarter-load only about 0.51.The curves of FIGURE 6 illustrate this. The reason for this improvementmay be summarized as follows: In the ordinary free turbine engine, toreduce power output below full power it is necessary to reduce fuel flowand, therefore, turbine inlet temperature of the gas generator isreduced. Operation at low temperature reduces the efficiency of the gasgenerator. While pressure ratio of the gas generator also decreasesbecause of reduction of speed, the efficiency of a regenerative engineis not affected much by this. By extracting useful work from thePatented Mar. 1, 1966 gas generator, the turbine temperature can bemaintained at the normal or full load temperature, as illustrated inFIGURE 8.

While the principal purpose of the invention is to improve part-loadfuel economy, an engine incorporating the invention has othersignificant advantages. The torque transmitting coupling between the twoturbines may eliminate the need for a free turbine governor, thussimplifying the fuel control. It also makes push starting of a vehicledriven by a free turbine or gas-coupled engine possible. The couplingbetween the two rotors may include provisions for dynamic braking of thevehicle.

We realize that mechanical coupling arrangements of one sort or anotherbetween the turbines of a free turbine engine have been proposed, eitherto allow the gas generator (or, more specifically, the compressor) toact as a dynamic brake on the power turbine shaft, or to transfer powerfrom the gas generator to the output shaft under conditions such thatthe gas generator turbine tends to overrun the power turbine. So far asWe are aware, however, there has been nothing providing the advantagesof our invention or including the principles thereof, that is, acting tomaintain a high substantially constant turbine temperature. The natureof the invention and its advantages will be apparent to those skilled inthe art from the succeeding detailed description of preferredembodiments of the invention.

Referring to the drawings, FIGURE 1 is a schematic diagram of aregenerative free turbine power plant with power transfer, including thecontrols.

FIGURE 2 is a sectional view of a power transfer clutch.

FIGURE 3 is a sectional view of a torque sensor.

FIGURE 4 is a schematic diagram of a portion of the control system,illustrating the structure of certain elements thereof.

FIGURE 5 is a typical map of overall performance of an engine as inFIGURE 1.

FIGURE 6 is a plot showing the effect of power transfer on fuel economy.

FIGURE 7 is a diagram of power transfer characteristics of a typicalengine.

FIGURE 8 is a chart showing the effect of power transfer upon turbineinlet temperature.

FIGURE 9 is a partial schematic diagram illustrating control of powertransfer directly by turbine temperature.

Referring first to FIGURE 1, the engine E is preferably, although notnecessarily, a regenerative engine of the known type described in US.patent applications Serial No. 559,475, filed January 16, 1956, nowabandoned; Serial No. 760,211 (Patent No. 3,077,074), filed September10, 1958; and Serial No. 127,079 (Patent No. 3,116,- 605 filed July 13,1961; all of common ownership with this application. These engines,developed and exploited by the assignee of this invention, have beenreported upon extensively in the technical literature. For this reason,and also because the present invention may be included in engines ofvarious structure, it is unnecessary to enlarge upon details of enginestructure. As shown schematically in FIGURE 1, the engine E includescentrifugal compressor 11, combustion apparatus 12, and a first tur bine13 coupled by a shaft 14 to the compressor. These structures are thebasic elements of the gas generator. The compressed air is dischargedfrom compressor 11 through a matrix 16 of a radial flow rotaryregenerator into the combustion apparatus 12. The exhaust gas from theturbine 13 flows through a second, load, or power turbine 17 supportedon a power output shaft 18. Turbine 17 exhausts through the matrix 16 tothe rear of a bulkhead 19 which divides the matrix into air flow and gasflow zones. Shaft 18 may be coupled to the load by a suitable gearbox ortransmisison 20. The engine is enclosed in a case or housing, indicatedgenerally at 21, to confine the motive fluid. The exhaust gas, afterpassing through the matrix 16, may be discharged to atmosphere throughan exhaust passage 22. This schematic shows only a single regenerator.Preferably, however, two are employed, disposed symmetrically inparallel as shown in the above-mentioned applications.

The primary control of the engine is of fuel flow to the combustionapparatus. Any appropriate fuel control 23 supplied with fuel by a pump24 may be employed. Suitable fuel controls are well known, and includingthis invention in an engine does not require any additions to the fuelcontrol.

Ordinarily, the vehicle operator controls the engine by a hand lever orfoot pedal, such as a throttle lever 26 connected to the fuel control.The fuel supplied by the pump 24 is delivered through line 27 to thefuel control, and the excess is returned to the pump inlet through line28, the engine fuel requirement being delivered to the combustionapparatus through line 29-. Such fuel controls ordinarily include one ormore fuel regulating or metering valves, which are variable throttlingvalves, and a head regulating valve which controls the metering pressuredifferential. They may include relief valves and various limiters orsafety valves. Fuel flow may be regulated to prevent overspeed,overtemperature, or lean blow-out but ordinarily is primarily responsiveto some such suitable parameter as compressor discharge pres! sure. Asindicated here, a line 31 pipes compressor discharge pressure into thefuel control. Such controls may include metering means responsive toengine speed and normally include governors to provide normal control oroverspeed protection, or both. This matter will be referred to later.

As so far described, there is a power plant comprising any suitable freeturbine engine and any convenient fuel supply and control meanstherefor. The pump 24 and other engine auxiliaries are ordinarily drivenby the gas generator. A chain of gears for tihs purpose may include adriving gear 32 on shaft 14, idler gear 33, coaxial united gears 34 and35, and a gear 36' on a main power transfer and accessory drive shaft37; Shaft 37, through power take-off gearing 38 and the obviousshafting, drives pump 24, a gas generator speed transducer or responsivedevice 39, and miscellaneous engine or vehicle auxiliaries indicated bythe block 41. An oil pump 42 is also driven by the power take-offshafting and gears 43.

With respect to the power transfer function, shaft 37 is connected byclutch 44 to shaft 45 and through a chain of transfer gears 46 to thepower turbine output shaft 18 and transmission 20. A speed transducer 47for indicating or control purposes may also be coupled to the powerturbine by gears 46.

The power transfer clutch 44 is. shown in detail in FIGURE 2. It ispreferably a multi-plate friction clutch in which the engaging forceand, therefore, the torque capacity, is determined by a hydraulicpiston. As will become apparent, such a clutch is merely representativeof various controllable torque-transmitting mechansims that may beemployed to couple the shafts 14. and 18. The clutch described isprovided for both power transfer and braking. Clutch 44 comprises a main'housing or case 51 and a front cover 52 suitably fixed together toprovide a housing for the multi-plate friction clutch 53 and supportsfor the driving and driven elements thereof. The input shaft 37 issupported by bearings, not illustrated, in the cylindrical forwardportion or nose 54' of the cover 52 The output shaft 45 is supported bya ball bearing 57 in the case, and the rear end of the input shaft issupported in the output shaft by needle bearing 58. The clutch 53includes a cage 59, the forward end of which constitutes a stub shaft 61supported by needle bearing 62 in the cover portion 54. The clutchfriction elements are contained by cage 59 and a flange 63 on theforward end of output shaft 45, this flange fixed in the cage by an ex-'panding snap ring 64. The cage 59 is slotted axially as indicated at 67to receive splines on clutch plates 68. Flange 63 also serves as aclutch plate. Friction disks 69, disposed between the clutch plates, areinternally splined for engagement with splines on the outer surface ofan inner clutch drum 71 coupled to shaft 37 by splines. Thus, the clutchplates must rotate with the output shaf and the friction disks with theinput shaft, and both are slidable axially of the shafts.

The clutch is engaged by a double hydraulic motor 70 which has twoeffective pistons defined by a single annular stepped piston 72. Thispiston is slidable in a stepped cavity bored in the cage 59 whichdefines an inner or power transfer cylinder 73 and an outer or brakecylinder 74. While it is not necessary to have two cylinders, it ispreferable to provide a larger cylinder area for braking the load thanfor power transfer, since the torque during braking may be five or moretimes the maximum power transfer torque. The rear face of the pistonengages the forward clutch plate 68'. Seals 76 are provided on thepiston 72 in the cylinders 73 and 74. The cylinders are single-acting,and clutch-releasing force is provided by a number of compressionsprings 77 received in sockets in the piston and in pockets in a springabutment ring 78 retained on the cage 59 by a snap ring- 79.

Oil under pressure is supplied to the power transfer cylinder 73 througha port 81 in the cover and passages 82, 83, and 84 in the cage 59. Oilunder pressure is supplied to the brake, cylinder 74 through a port 86in the cover and passages 87, 88, and 89 in the cage. The ports aresealed off by piston ring seals 91. Since the clutch is operated as aslipping clutch, a flow of cooling oil is provided. This oil is suppliedthrough a port 92 and flows through the annular passage 93 between theshaft 37 and the cage (defined in part by sleeve 94 in the cage) to theinner clutch drum 71. 'It then flows through gaps or notches 95 in therim of the inner clutch drum, between the clutch plates and the frictiondisks (which are grooved), through the slots 67 in the cage into thehousing 51, and is vented through a port 96. The cooling oil is suppliedunder pressure and circulation is aided by centrifugal force due torotation of the clutch.

The torque transferred by the clutch will be closely proportional to theengaging force exerted by piston 72. This, in turn, is proportional tothe sum of the products of the pressures in .the cylinders 73' and 74 bythe effective piston areas minus the force of springs 77. The cylinder74 is used only to provide a high degree of friction to transmitrelatively large amounts of power from the power turbine to thecompressor to brake the output shaft. Cylinder 73 is supplied fluidunder controlled pressure to determine the amount of torque transmittedin normal opera-tion of the turbine at part-load. It is also energized.to assist in providing clutching force for braking, along with cylinder74.

Returning to the schematic diagram of FIGURE 1, the oil which issupplied to clutch 44 is circulated under pressure by pump 42 driven bythe gas generator. This oil is drawn from a source such as a sump 101through a line 102 and the pressure is limited by a suitable reliefvalve 103.- Pump 42 may supply oil for engine lubrication through line194 or it may be independent of the, lubricating system. The clutchcooling oil is supplied through line 106 to port 92. of the clutch 44.Pump 102. also supplies oil for control and servo purposes, the pres-.sure of which is held constant by a constant pressure, regulating valve107 which discharges into a supply line 108.

One of the basic elements of control of power trans-. fer in the systemof FIGURE 1 is a torque sensor 111,, illustrated in FIGURE 3. The torquesensor res ond 1 the torque transmitted through the intermediate gears34, 35 from the gas generator turbine to the several auxiliary and powertransfer shafts. Gears 34 and 35 are integral with a torquemeter shaft112 mounted in ball bearings 113 and 114. Bearing 114 is mounted in atorque sensor body 116 and bearing 113 in a cover 117. The gears 34 and35 are helical and of opposite hand helix angles so that an axial thrustis developed on the shaft 112 proportional to the torque transmitted.Shoulders 118 and 119 on the shaft may engage the inner races of thebearings 113 and 114, and permit some axial movement of the shaft. Anysuch axial movement is communicated through a ball thrust bearing 121 toan openended cylinder 122 reciprocably disposed in a block 123 fixed tothe body 116. A setscrew 124 engaging a key- Way 126 in the cylinderprevents rotation of the cylinder. The cylinder 122 has a steppedinternal bore with a smaller diameter portion 127 and a larger diameterportion 128. The cylinder is guided on a fixed stepped piston 129 havinga flange which is fixed to the right end of block 123 with a gasket 131between. The fixed piston 129 includes a larger diameter portion 132which acts as a pistont with the portion 128 of the cylinder, the twodefining a pressure chamber 133 between them. The smaller diameterportion 134 of the piston constitutes one member of a valve, the othermember of which is the cylinder 122.

Controlled pressure servo oil supplied by regulating valve 107 throughline 188 enters the torque sensor through a port and passage 136 whichcommunicates through a small radial port 137 with the outer surface ofthe piston. A groove 138 in the cylinder connects through a port 139with the chamber 133. The helix angles of gears 34 and 35 are such thattransfer of power from the shaft 14 through gears 34 and 35 biases theshaft 112 to the right as illustrated and tends to contract the chamber133. This rightward movement permits variable registry between port 137and groove 138 to supply fluid under pressure to chamber 133 to resistthe torque-induced thrust. The pressure in chamber 133, therefore, isproportional to torque. An orifice passage 140 bleeds chamber 133 at aslow rate continuously and allows the pressure in the chamber todecrease when the torque is reduced. A passage 141 through piston 129provides the output of pressure through a line 142. This pressureprovides the torque input to means which control the power transferclutch 44.

Passage 136 terminates in a jet 143 from which oil is squirted through asleeve 144 into a central bore 146 in the torquemeter shaft 112. Radialpassages 147 carry the oil to the axially slidable journals of the shaftin the bearings 113 and 114. Since normal torque urges cylinder 122toward piston 129, a reversal of torque, which occurs when the externalload device tends to drive the power turbine and causes it to outrun thegas generator turbine, urges the shaft 112 and cylinder 127 to the leftas illustrated. This movement is not opposed by hydraulic pressure, butis terminated when abutment 118 engages the thrust bearing 113. Thismovement of the cylinder in response to reverse torque brings a recess148 in the cylinder 122 into registry with a radial port 149 in thepiston supplied with pressure oil through passage 136. Recess 148 alwaysregisters with an axially elongated port 151 in the piston which isconnected by a passage 152 to an output line 153 which energizes theclutch 44 for engine braking. When the torque is in the normaldirection, the position of cylinder 122 is such that passage 152 andport 151 communicate through groove 148 with a drain port 154 in thecylinder which leads through passage 156 and a line 157 to the sump.

Under torque reversal, port 138 is moved out of registry with port 137and pressure in chamber 133 drops to zero. Thus, a no torque signal(zero pressure) is transmitted through line 142. This signal actsthrough the torque programer (to be described) to cause full oilpressure to be applied in clutch cylinder 73 in addition to cylinder 74.The maximum piston area is thus available to lock up the clutch so as totransmit a torque corresponding to a desired large fraction of enginepower rating, such as about 60% thereof.

In normal running, the power transfer clutch 44 is controlled totransmit a desired value of torque by comparing the measured torque fromthe torque sensor 111 with a desired torque or power transfer signalfrom a torque programer 161. The torque programer is an automatic valvewhich controls the power transfer clutch piston in response to inputs ofactual torque output of the gas generator and actual speed of the gasgenerator. It acts upon oil supplied by pump 42 to clutch 44. The torquesensor pressure is transmitted through line 142 as explained above. Thespeed signal is a fluid pressure signal transmitted through line 162from the speed transducer 39, the structure of which will be described.Servo oil at controlled pressure is supplied through line 108.

The torque programer 161 (FIGURE 4) comprises a valve body 163 and acontrol cylinder 164 mounted rigidly together. A cylinder 166 in thevalve body mounts a servo oil control spool 167 and a cam follower 168.A compression spring 169 is mounted between the valve spool and camfollower. Servo oil from line 108 enters the valve through port 171which intersects the wall of bore 166 in position to be variablethrottled by valve spool 167. An outlet port 172 is connected through aline 173 and other devices, to be described, to the power transfercylinder 73 of clutch 44. The torque sensor signal pressure in line 142is admitted to a chamber 173 where it biases the valve in the directionto cut off clutch servo oil. This bias is opposed by the force of spring169. The cam follower 168 includes a follower roller 174 and a clevisedend 176 which straddles a cam 177. This cam lies between a piston 178and a guide and spring seat 179, all of these being integral. The cam177 has a suitably contoured surface which engages the follower 174. Cam177 is guided in a bore 182 in the cylinder body 164 by piston 178 andspring seat 179. It is biased upwardly, as illustrated, by compressionspring 183 and biased downwardly by the gas generator speed signalsupplied through line 162 into the chamber 184 above the piston 178. Ahead 186 closes this chamber. The space below spring seat 179 is ventedthrough a passage 187 into the chamber which contains the cam followerwhich, in turn, is drained through a passage 188 into a port 189connected to the sump. A clutch cylinder drain passage 191 connects tothe sump port and cooperates with a land of the valve spool 167. If thetorque signal moves the valve spool 167 to the left, the supply of servooil will be shut off and servo oil will be drained from the clutchthrough passage 191.

It will be seen that the torque programer valve supplies servo oil to orbleeds it from the clutch 44, thus varying the torque, and the amount oftorque transferred is one factor which determines the operation of thisvalve. The other factor is gasifier speed. Through the action of cam177, .a definite loading of spring 169 is established for each value ofgas generator speed. The clutch will therefore 'be controlled tomaintain the transfer shaft torque ouput of the gas generator at a valuewhich is a function of speed related to the characteristics of theparticular engine so that turbine temperature is maintainedsu'bstanially constant at varying power levels. The contouring of thecam may be determined by calculation or experiment for any particularengine. It will be seen that the no torque signal upon torque reversalwill always open valve 167 to supply oil to line 173 regardless ofengine speed.

The structure so far described, plus lines to conduct the actuating oilto the clutch, constitutes a complete operating system. However, certainadditional devices preferably included in the system are illustrated andwill now be described. First, acceleration valve 201, interposed in theline from the torque programer to the clutch,

which improves the acceleration of the engine. Since the effect of thetorque programer is to maintain a high turbine temperature at partloads, there is not much margin for addition of fuel to accelerate thegas generator, both with regard to turbine temperature limits and thecompressor surge threshold. The compressor operates closer to the surgeline during power transfer. This is desirable to increase runningefiiciency, but it impedes acceleration. If the engine is running atlight load, the gas generator will be turning well below full speed. Toassume full load or to accelerate the load rapidly, it is necessary toaccelerate the gas generator to full speed. This can be facilitated bytemporarily cutting out the power transfer so that all of the power ofthe gas generator is available to accelerate it. While various meansmight be adopted, the acceleration valve 201 as illustrated is verysimple and suitable for this purpose. This valve responds to substantialpower increasing movements of the power control lever 26 to release orunload the power transfer clutch. It is not affected by small or slowmovements.

The acceleration valve 201 includes a valve body 202 having a bore 203coaxial with a second bore 204 of slightly larger diameter. A valvespool 206 slidable in the bore 204 normally abuts the shoulder at theend of the bore. A spring abutment 207 is slidable in the bore 203, anda compression spring 208 is retained between this and the valve spool.Spring 2015 biases the spool 206 to the right, as illustrated, inopposition to oil pressure in chamber 209 indicative of gas generatorspeed supplied from the speed transducer 39 through line 162. Chamber209 is closed by a head 2'11 and the other end of the valve body isclosed by a head or cap 212. Abutment 207 bears against an eccentric orcam 213 on a shaft 214 rotated in the body by an arm 215. Arm 215 isconnected by any suitable means, indicated by the broken line 217(FIGURE 1) to the throttle or power control lever 26. The throttlesetting or gas generator speed request thus, through cam 213, determinesthe loading of spring 208 biasing valve spool against the pressure inchamber 209 determined by actual gas generator speed. In normaloperation of the engine, the speed signal is suflicient to hold thespool against the shoulder in the bore, or substantially in thisposition. Power transfer clutch control line 173 enters the valve bodythrough a port 21 8 which aligns with a groove 219 of the valve spool inthis position. Communication is thus maintaned between the torqueprogramer and a port 221 of the acceleration valve which connects to aline 222 leading to the power trans fer cylinder of clutch 44. Anincrease in the loading of spring 208 tends to move value spool 206 tothe rig-ht to bring groove 219 into registry with a bleed port 223connecting through outlet 224 to the sump. Slight movements of thethrottle lever 26 will not shift the valve spool sufficiently to drainthe clutch cylinder, but more substantial differences between the speedsetting and actual speed will release fluid from the clutch, thusunloading the gas generator and improving its acceleration. The chamberswithin the bore 203 are vented to the sump through pa-ssages 226 and227.

A further desirable element of the system is a clutch overtemperaturevalve. The purpose of this valve is to release or relieve the clutchingor braking effort in response to too great generation of heat in theclutch. If the clutch should be subjected to too heavy a load at toogreat a slip rate, excessive heat generation might damage the clutch.For this reason, an automatic valve responsive to the temperature ofcooling oil leaving the clutch may be connected in circuit with thebrake and clutch cylinder energizing lines. The cooling oil dischargedfrom the clutch through port 96 flows through a line 231 to the clutchovertemperature valve 232 and is discharged from this valve to the sump.The power transfer clutch energizing line 222 enters the valve 232 andis connected through it to a line 233 leading to the clutch. The brakeenergizing oil line 153 is connected through the overtemperature valveto line 234 which connects with port 86 of the clutch.

The overtemperature valve is simply a balanced spool valve responsive tocooling oil temperature and movable to cut off the two lines which carryservo oil to the clutch. The valve includes a body 236 having a bore 237within which is mounted the three-land spool 238. The spool is biased inthe direction to permit oil flow by a coil spring 239 acting against anadjustable abutment 241. An oil temperature responsive capsule 242 ismounted between the body 236 and a head 240 which closes the valve bore.This capsule is a known temperature-responsive device which includes apin 243 projected in response to increase in the temperature of thecapsule. The capsule is exposed to cooling oil discharged from theclutch through line 231 flowing through a chamber 244 in the head andout to the sump through a port 246. Transfer clutch oil line 222 isthrottled and closed by the lower land 247 of the valve upon upwardmovement thereof. Similarly, the brake-engaging fluid line 153 may bethrottled and closed by the middle land 248 of the spool. Upon movementof the valve to cut off flow to the clutch, the clutch cylinders arevented to ports 25 1 and 252, respectively, which are connected to thedrain line 246. The ends of the valve chamber above and below the spoolare also drained into the sump. The overtemperature valve is merely asafety device responsive to conditions indicative of possible clutchdamage. Such might occur because of misoperation of the engine resultingin very heavy clutch slippage.

It will be appreciated that the need for an overtemperature clutchrelease will depend upon the nature of the engine installation,controls, and load. Controls may be provided to disengage the clutch indirect response to the rate of slip; that is, the difference in speed ofthe clutch input and output shafts.

Also, if a load such as a vehicle is driven through a step transmission,the transmission may be downshifted in response to low power turbinespeed, or low speed relative to the gas generator, thus permitting thepower turbine to increase speed when slip approaches excessive values.

Some means to respond to gas generator speed is necessary in the systemof FIGURE 1. One device suitable for this purpose is the speedtransducer 39 illustrated in FIGURE 4. This is a known type ofcentrifugal force responsive throttling valve. As illustrated somewhatschematically, the speed transducer 39 includes a body 262 Which has anend cover 263, the two parts defining a chamber 264. A shaft 266 ismounted in the two parts of the body by bearings 267 and 268 suitablysealed. A rotor 271 pinned to the shaft 266 defines a radial valvecylinder 272 within which a cylindrical plug or flyweight 273 isreciprocable. Valve member 273 may approach an outlet 274 from the rotorand is biased toward the outlet by a compression spring 276. Oil fromthe regulating valve 107 is supplied through line 108 to a port in thebody and through an orifice 2.77 which is of less diameter than outlet274. After passing through the orifice 277, the oil may flow either froma port 278 into the speed sense line 162 or through a passage 279 to agroove 281 surrounding the shaft 266. Radial ports 282 and a pas sage283 in the shaft, and a passage 28 4 in the rotor conduct the coil tothe outer end of cylinder 272. There is normally no significant flowthrough line 162, but there is flow from the regulated pressure line 108through the orifices 277 and 274 in series. When the shaft isstationary, the pressure in line 162 is low, as the oil readily escapesthrough port 274 and from the chamber 264 to the sump. However, as thespeed of rotation of the rotor increases, the centrifugal force actingon the valve member 273 moves it outward, throttling port 274 until thepressure in cylinder 272 balances the centrifugal force. Thus, theaction of centrifugal force will build up a pressure in line 162proportional to the square of engine speed.

This particular speed responsive transmitter is merely one of manydevices which could be used. Among others which appear desirable forthis purpose is the speed sensor disclosed in application Serial No.2,265 (Patent No. 3,039,315), filed January 13, 1960, of commonownership with this application. It is a dynamic head pickup operatingupon the Pitot tube principle within an annulus of oil rotated by theturbine. A centrifugal pump may also be used to develop aspeed-responsive pressure. It will be apparent that the generalcombination is independent of the particular speed responsive device,and that any suitable means for providing a sense of turbine speed tothe cam of the torque programer and to the acceleration valve may beemployed.

The speed transducer 47 for the power turbine may be of any suitabletype, and may be identical to the transducer 39. The transducer 47receives servo oil through line 108 and transmits a speed pressurethrough line 291 to the fuel control 23. In an engine incorporatingpower transfer, the power turbine speed input to the fuel control may beomitted, or it may be retained as an additional safety feature. Also, itmay provide a means for controlling the power transfer clutch orshifting the transmission.

With some types of speed sensors, the regulated pressure supply line 108would not be necessary. For example, the speed transducer described inapplication Serial No. 2,265 (Patent No. 3,039,315) operates fromlubricating oil which is not under pressure.

Another element which may improve this system, under some conditions atleast, is means for modifying the schedule of power transfer as afunction of air temperature. It is well known that the turbine inlettemperature of a gas turbine engine increases with increases in ambientair temperature. For constant turbine temperature, fuel and thereforepower must be reduced as air temperature increases. The system so fardescribed is quite readily modified in one way or another to make thetorque transfer schedule a function of ambient temperature, which isdesirable to make the gas generator turbine inlet temperatureinsensitive to ambient temperature. The preferred mode of accomplishingthis in the system of FIG- URE 1 lies in means for varying the value oftorque transmitted from the torque sensor to the torque programer byaction of a temperature compensator. The temperature compensator 301 isconnected so as to bleed oil from the line 142 through a branch line302. In addition, if the temperature compensator is employed, arestriction 303 is provided in the line 142 upstream of the branch line302. Restriction 303 allows a pressure drop to be created in line 142 asoil is bled from it by compensator 301. The compensator 301 includes abody or housing 304 within which the needle valve 306 variably throttlesthe passage from inlet line 302 to an outlet or sump port 307. Thisvalve needle is reciprocated by a stack of dished bimetal disks 309, aknown temperature responsive device. The bimetal elements 309, if theyare exposed to ambient atmospheric or engine inlet temperature, move toopen the valve and thus reduce the torque sense by the additional dropthrough orifice 303 as air temperature decreases. By thus reducing thetorque sense, the valve spool 167 closes off the supply of pressure oilto the power transfer clutch at a higher value of torque as airtemperature decreases. The result is that the level of power transfervaries reversely to inlet or ambient air temperature.

If desired, the temperature compensator 301 may include means foradjusting its action represented by the rotatable knob 310 on a shaft311 threaded in the housing 301, which may shift the stack of bimetaldisks and the needle valve axially, thus adjusting the turbinetemperature setting of the temperature-responsive valve.

This completes the description of the structure of the system of FIGURE1 and its elements. The operation 10 should be clear from the foregoing,but it may be desirable to review the operation briefly and, in sodoing, to refer to the curves of FIGURES 5 to 8. Assume that the engineis running normally, for example, at a minimum idling power level; thegas generator turbine 13 drives the auxiliaries including the speedtransducer 39. Under these idling conditions, a little gas horsepower isavailable to the power turbine, and it may rotate idly or may bestationary, if the load is coupled to it. The power transfer clutch 44will be open. To extract substantial power from the engine, the gasgenerator must be accelerated by increasing the fuel rate so as toprovide more gas energy to the power turbine. Above a low idle speed,the control system begins, through cam 177, to engage the power transferclutch.

The nature of the characteristic for a typical 265 HR engine with powertransfer is shown in FIGURE 5. It will be noted that the output shafthorsepower is relatively low below 70% gas generator speed but increasesrapidly in the higher range of gas generator speed up to which is thenormal maximum gas generator speed. The power also increases with powerturbine speed but levels ofi. at the higher power turbine speeds. Theline indicated as power transfer clutch locked up represents thecondition under which the power turbine tends to overrun the gasgenerator turbine and the power transfer clutch is strongly engaged tobrake the power turbine, and thus the load. To the left of this line,the power transfer clutch slips under controlled torque. The curves ofFIGURE 5 also include lines of specific fuel consumption, from which itwill be apparent that very good values of specific fuel consumption aremaintained down to relatively low output shaft speeds and power output.

The effect of power transfer on fuel economy of the engine is alsoillustrated by FIGURE 6, in which the solid line illustrates variationin specific fuel consumption with horsepower output, and the dotted lineshows the variation in fuel consumption in an otherwise identi calengine lacking the power transfer feature. The much lower fuelconsumption at part load with power transfer is apparent.

The order of magnitude of power transfer in an engine of this size canbe seen in FIGURE 7, which illustrates by the curves the amount ofhorsepower transferred, including that directed to the auxiliaries, andthe torque. The actual value of torque will depend, of course, upon theoverall ratio of the gearing between the turbine shaft and the powertransfer clutch. This particular curve is for a 6.9 to 1 ratio of gasproducer speed to clutch speed. The effect of this power transfer onturbine inlet temperature is illustrated for this typical engine in FIG-URE 8. As will be seen, the turbine inlet temperature will remainconstant at 1700 over a range of gas producer speed down to 60%,whereas, without power transfer, it falls off rapidly and is down to1250 at 70% gas producer speed.

When the temperature is kept at the high level, the effiicency of theengine is greatly improved. The speed of the gas generator decreasesand, with it, the compression ratio, but maintenance of the hightemperature prevents the normal increase in specific fuel consumption.The power taken from the gas generator turbine is, of course, usable topropel a vehicle or drive any other load. This system is particularlyadvantageous with regenerative gas turbines, since the efficiency of aregenerative engine is not sensitive to compressor pressure ratio.However, it is useful in a non-regenerative engine, although not to sucha great extent.

It is ordinarily desirable, when power transfer is controlled by ameasurement of mechanical power delivered by the gas generator, thatthis measurement include auxiliary power. Usually, the power requiredfor auxiliaries is significant and is variable. If the auxiliary powerload is not taken into account, measurement of power transfer torqueaffords a less accurate means of holding turbine temperature at thedesired point. However, if the auxilary load is constant or isinsignificantfor example, auxiliaries could be driven by an independentpower source-then it is not necesary to include auxiliary torque in themeasurement of torque used to control the power transfer clutch. Itshould also be borne in mind that power transfer may be controlled byother means, as for example, directly by turbine temperature, in whichcase no measurement of torque is required. Other factors might be usedto control transfer of power, the point being that the power transfer iscontrolled so that sufiicient power is taken from the gas generator tokeep the normal high full load operating temperature down to low valuesof load. In fact, it is feasible to increase turbine temperatureslightly at low power where rotational speed and therefore stresses arelower.

Referring specifically to the system of FIGURE 1, in the operation ofthe engine the power level is determined by the manual lever 26 whichcontrols fuel supply. The power transfer clutch extracts some power fromthe gas generator turbine and assists the power turbine in driving theload through transmission 20. The speed of the gas generator is measuredby the transducer 39 which may provide a speed signal to the fuelcontrol and provides a speed signal to the torque programer 161 and theacceleration valve 201. The torque sensor 111 provides a torque signalthrough line 142 to the torque programer, which signal may be trimmed orcompensated for air temperature by the temperature compensator valve301, if it is provided. The torque programer acts to control thepressure of fluid to the power transfer clutch, adjusting the pressureso that the torque extracted from the gas generator equals thatprogramed or scheduled by the torque programer as a function of enginespeed.

Since, in the embodiment of the invention described above, the amount oftorque load which may be assumed by the gas generator is determined as afunction of the speed of the gas generator, it is necessary to controlthe power transfer clutch to transfer an amount of torque which is afunction of the speed of the gas generator. This relation is indicatedby the torque curve in FIGURE 7. Therefore, the torque sensor measuresthe torque taken from the gas generator, the speed transducer measuresthe speed of the gas generator, and the torque programer adjusts thefriction of the power transfer clutch to make the torque derived fromthe gas generator equal that scheduled as a function of gas generatorspeed. Specifically, this speed schedule is embodied in the contour ofthe cam 177 of the torque programer which, in effect, provides an inputof desired torque into the programer which in turn adjusts the clutchoil pressure to make the torque output equal that desired.

Since the high gas temperature under power transfer inhibits rapidincrease in power capacity of the engine, an acceleration valve 201 isdesirable in many cases to disengage, or reduce the torque transmittedby, the power transfer clutch so that fuel supplied to the gas generatormay accelerate it to a higher speed consonant with a higher engineoutput level. The acceleration valve acts in response to substantialdifferences between the speed called for by the control 26 and theactual speed of the gas generator. It may also be desirable to providethe clutch overtemperature valve 232 to relieve the pressure on theclutch in case of overheating.

In many cases, it is also highly desirable to provide positive means tobrake the load and also to provide a positive restraint on overspeed ofthe power turbine when there is no load or upon disengagement of theturbine from the load, for instance. This is accomplished through thesame power transfer clutch by energizing it in response to overrunningof the gas generator by the power turbine, or power flow from the powerturbine back to the gas generator, so that the compressor 11 can bedriven by the shaft 18. The amount of reverse torque transmitted duringbraking ordinarily needs to be limited, out of regard 12 to the strengthof the transfer gear installation. Obviously, the ratio of speeds 'ofthe two turbines during braking may be any appropriate value, as theratio of the gears coupling the turbine shafts to the clutch may be asdesired.

While the slipping clutch is not the most efiicient means to transferpower from the gas generator to the load, since any slip represents somepower loss, its simplicity, reliability, and ease of control recommendit. Obviously, there are many types of power transmission devices whichcan be controlled in response to a signal directly or indirectlyrepresenting a factor such as input torque, engine temperature, enginespeed, or the like, so as to transfer torque to the extent to maintaingas generator turbine temperature at a high level conductive to bestefliciency and which permit variations in the speed ratio of the twoturbines.

In this connection, FIGURE 9 is a fragmentary view of a portion of thesame engine as FIGURE 1, but illustrating an electrically controlled oroperated clutch 320 connecting shafts 37 and 45. Such a clutch might bea magnetic particle clutch, a slip clutch engaged magnetically, anelectrically controlled servo-operated clutch, or various known types ofelectrodynamic power transmission mechanisms. Such a clutch might becontrolled in response to engine speed and torque as described inconnection with FIGURE 1, but, in FIGURE 9, it is shown as controlled inresponse to temperature of the motive fluid measured by one or morethermocouples 322 in the turbine inlet. As is well known, turbinetemperature may also be measured in the turbine exhaust. Suchthermocouples rnay operate through voltage and power amplifier devicesindicated by the amplifier 324 to control substantial amounts of power.As indicated, the amplifier is energized from a current source throughlines 326, is controlled by thermocouple 322, and supplies power throughlines 328 to control the clutch 320. It is clear that a temperaturemeasuring device also could control a hydraulic clutch. Electricallycontrolled pressure regulating valves are known; also, temperatureresponsive pressure regulating valves which might respond directly toturbine temperature. However, measurement of turbine temperature is notas satisfactory for our purposes as measurement of speed and torque,because of the long response time of most temperature sensitive devices,and for other reasons.

The foregoing description of preferred embodiments of our invention willmake its principles and advantages clear. This description is not to beconstrued as limiting the scope of the invention, as many modificationsof structure and organization may be made within the principles thereof.

We claim:

1. A gas turbine power plant comprising, in combination, a gas generatorincluding a compressor, combustion apparatus, and a turbine driving thecompressor, a load turbine gas-coupled to the gas generator,controllable torque-transmitting means coupling the turbines includingmeans controlling the amount of torque transmitted, and means responsiveto a condition of the gas generator indicative of torque available fromthe gas generator as shaft power within allowable limits of gasgenerator turbine temperature connected to said torque controlling meansto control the torque transmitted so as to load the gas generatorturbine variably with decrease in engine power level to maintain a highgas generator turbine temperature at light loads.

2. A power plant as recited in claim 1 in which the torque-transmittingmeans includes a slip clutch and the means to control the torquetransmitted varies the torque capacity of the clutch.

3. A power plant as recited in claim 1 in which the said condition isgas generator turbine speed.

4. A power plant as recited in claim 1 in which the said condition isturbine motive fluid temperature.

5. A power plant as recited in claim 1 including a heat exchangerconnected to transfer heat from the turbine exhaust to the compressordischarge air.

6. A power plant as recited in claim 1 including means for controllingengine fuel supply and means responsive to movement of the fuelcontrolling means to accelerate the gas generator coupled to thetorque-transmitting means so as to temporarily reduce the torquetransmitted and thereby facilitate acceleration of the gas generator.

7. A gas turbine power plant comprising, in combination, a gas generatorincluding a compressor, combustion apparatus, and a turbine driving thecompressor, a load turbine gas-coupled to the gas generator,controllable torque-transmitting means coupling the turbines includingmeans controlling the amount of torque transmitted, and means responsiveto a condition of the gas generator indicative of torque available fromthe gas generator as shaft power within allowable limits of gasgenerator turbine temperature connected to said torque controlling meansto control the torque transmitted so as to load the gas generatorturbine variably with decrease in engine power level to maintain a highgas generator turbine temperature at light loads, brake control meansoperative to control the torque-transmitting means to a torque levelsuflicient for substantial braking of the load turbine, and meansresponsive to transfer of torque from the load turbine to the gasgenerator turbine effective to operate the brake control means.

8. A power plant as recited in claim 7 in which the torque-transmittingmeans includes a slip clutch and the means to control the torquetransmitted varies the torque capacity of the clutch.

9. A gas turbine power plant comprising a first turbine, a compressordriven thereby, a power output second turbine rotatable independently ofand in motive fiuid circuit with the first turbine, means includingcombustion apparatus connecting the compressor to the turbines, andmanually settable fuel supply and regulating means connected to thecombustion apparatus, in combination with power transfer meansmechanically interconnecting the turbines, the power transfer meanscomprising a controllable variable-ratio torque-transmitting couplinghaving an input element constantly coupled to the first turbine forrotation therewith and an output element constantly coupled to thesecond turbine for rotation therewith, a torquemeter connected tomeasure torque delivered by the first turbine to the input element,torque scheduling means responsive to a condition of engine operationindicative of surplus torque available from the first turbine at normalrated temperature, and coupling control means responsive to thetorquemeter and the scheduling means and operable upon the coupling tovary the torque transmitted thereby to balance the torque delivered withthe torque available.

10. A power plant as recited in claim 9 including a heat exchangerconnected to transfer heat from the turbine exhaust to the compressordischarge air.

11. A power plant as recited in claim 9 including engine auxiliariesdriven by the first turbine and in which the torquemeter is connected tomeasure a torque including that delivered to the said auxiliaries.

12. A power plant as recited in claim 9 in which the torque-transmittingcoupling is a variably loadable friction clutch.

13. A gas turbine power plant comprising a first turbine, a compressordriven thereby,a power output second turbine rotatable independently ofand in motive fluid circuit with the first turbine, means includingcombustion apparatus connecting the compressor to the turbine, andmanually settable fuel supply and regulating means connected to thecombustion apparatus, in combination with power transfer meansmechanically interconnecting the turbines, the power transfer meanscomprising a controllable variable-ratio torque-transmitting couplinghaving an input element constantly coupled to the first turbine forrotation therewith and an output element constantly coupled to thesecond turbine for rotation therewith, a torquemeter connected tomeasure torque delivered by the first turbine to the input element,torque scheduling means responsive to a condition of engine operationindicative of surplus torque available from the first turbine at normalrated temperature, coupling control means responsive to the torquemeterand the scheduling means and operable upon the coupling to vary thetorque transmitted thereby to balance the torque delivered with thetorque available, and acceleration override means responsive to acondition indicative of a substantial engine acceleration signalconnected to the coupling effective to reduce the torque transmittedthereby during said condition.

14. A gas turbine power plant comprising a first turbine, a compressordriven thereby, a power output second turbine rotatable independently ofand in motive fluid circuit with the first turbine, means includingcombustion apparatus connecting the compressor to the turbines, andmanually settable fuel supply and regulating means connected to thecombustion apparatus, in combination with power transfer meansmechanically interconnecting the turbines, the power transfer meanscomprising a controllable variable-ratio torque-transmitting couplinghaving an input element constantly coupled to the first turbine forrotation therewith and an output element constantly coupled to thesecond turbine for rotation therewith, a torquemeter connected tomeasure torque delivered by the first turbine to the input element,torque scheduling means responsive to a condition of engine operationindicative of surplus torque available from the first turbine at normalrated temperature, coupling control means responsive to the torquemeterand the scheduling means and operable upon the coupling to vary thetorque transmitted thereby to balance the torque delivered with thetorque available; and means responsive to an ambient conditionindicative of engine power capability effective to modulate the torquetransmitted as a function of the said ambient condition.

15. A gas turbine power plant comprising a first turbine, a compressordriven thereby, a power output second turbine rotatable independently ofand in motive fluid circuit with the first turbine, means includingcombustion apparatus connecting the compressor to the turbines, andmanually settable fuel supply and regulating means connected to thecombustion apparatus, in combination wit-h power transfer meansmechanically interconnecting the turbines, the power transfer meanscomprising a controllable variable-ratio torque-transmitting couplinghaving an input element constantly coupled to the first turbine forrotation therewith and an output element constantly coupled to thesecond turbine for rotation therewith, a torquemeter connected tomeasure torque delivered by the first turbine to the input element,torque scheduling means responsive to a condition of engine operationindicative of surplus torque available from the first turbine at normalrated temperature, coupling control means responsive to the torquemeterand the scheduling means and operable upon the coupling to vary thetorque transmitted thereby to balance the torque delivered with thetorque available; braking control means in the torquemeter responsive totorque transmitted from the second turbine to the first turbine throughthe coupling, and means actuated by the braking control means to controlthe torque capacity of the coupling to a value substantially higher thanthe greatest aforementioned excess torque to provide for braking thesecond turbine by power transfer to the compressor.

16. A gas turbine power plant comprising a first turbine, a compressordriven thereby, a power output second turbine rotatable independently ofand in motive fluid circuit with the first turbine, means includingcombustion apparatus connecting the compressor to the turbines, andmanually settable fuel supply and regulating means con- :15 nected tothe combustion apparatus, in combination with power transfer meansmechanically interconnecting the turbines, the powertransfer meanscomprising a controllable variable-ratio torque-transmitting couplinghaving an input element constantly coupled to the first turbine forrotation therewith and output element constantly coupled to the secondturbine for rotation therewith, a torquemeter connected to measuretorque delivered by the first turbine to the input element, torquescheduling means responsive to a condition of engine operationindicative of surplus torque available from the first turbine at normalrated temperature, coupling control means responsive to the torquemeterand the scheduling means and operable upon the coupling to vary thetorque transmitted thereby to balance the torque delivered with thetorque available; acceleration override means responsive to a conditionindicative of a substantial engine acceleration signal connected to thecoupling effective to reduce the torque transmitted thereby during saidcondition; means responsive to an ambient condition indicative of enginepower capability effective to modulate the torque transmitted as afunction of the said ambient condition; braking control means responsiveto overrunning of the first turbine by the second turbine, and meansactuated by the braking control means operable to control the torquecapacity of the coupling to a value substantially higher than thegreatest aforementioned excess torque to provide for braking the secondturbine by power transfer to the compressor.

17. A gas turbine engine of the shaft power output type comprising, incombination, a power output turbine having a power output shaft; a gasgenerator including a compressor, combustion apparatus supplied by thecompressor, and a turbine energized by the combustion apparatusconnected to drive the compressor, the gas generator supplying motivefluid to the power output turbine; means for controlla'bly supplyingfuel to the combustion apparatus, the rate of fuel supply determiningthe output of the gas generator and thereby the energy level of thepower output turbine; and means for transferring mechanical energy fromthe gas generator turbine to the power output shaft so as to maintainturbine temperature of the gas generator substantially constant over awide range of energy levels of the power output turbine, the lastrecitedmeans including a torque-transmitting coupling of an impositive typeallowing progressive variation in the relative speeds of the twoturbines, and means responsive to a condition of the gas generatorindicative of gas generator turbine energy level controlling themagnitude of the torque transmitted by the coupling.

18. A gas turbine engine of the shaft power output type comprising, incombination, a power output turbine having a power output shaft; a gasgenerator including 2.

compressor, combustion apparatus supplied by the com- ,7

pressor, and a turbine energized by the combustion apparatus connectedto drive the compressor, the gas generator supplying motive fluid to thepower output turbine; means controllably supplying fuel to thecombustion apparatus, the rate of fuel supply determining the output ofthe gas generator and thereby the energy level of the power outputturbine; and means for transferring mechanical energy from the gasgenerator turbine to the power output shaft so as to maintain turbinetemperature of the gas generator substantially constant over a widerange of energy levels of the power output turbine, the last mentionedmeans comprising an impositive torque-transmitting coupling between theturbines, a transfer control operable to progressively vary the energytransferred by the coupling, and means responsive to a condition of thegas generator indicative of gas generator turbine temperature coupled tothe transfer control to control the energy transferred so as to mainsubstantially full-load gas generator temperature as the energy levellevel,

19. A gas turbine engine of the shaft power output type comprising, incombination, a power output turbine having a power output shaft; a gasgenerator including a compressor, combustion apparatus supplied by thecompressor, and a compressor turbine energized by the combustionapparatus connected to drive the compressor, the compressor turbinebeing of sufficient capacity to drive the compressor at maximum ratedspeed and having excess capacity at lower speeds of the compressor, thegas generator supplying motive fluid to the power output turbine; meansfor controllably supplying fuel to the combustion apparatus, the rate offuel supply determining the output of the gas generator to the poweroutput turbine; and means for transferring mechanical energy from thecompressor turbine to the power output shaft so as to maintaincompressor turbine temperature substantially constant over a wide rangeof energy levels of the power output turbine, the last-recited meansincluding a torque-transmitting coupling of an impositive type betweenthe turbines allowing progressive variation in the relative speeds ofthe two turbines, a transfer control operable to vary progressively thetorque transferred by the coupling, and means responsive to a conditionof the gas generator indicative of compressor turbine excess torquecapacity as limited by compressor turbine temperature coupled to thetransfer control too control the energy transferred so as to maintainsubstantially full-load compressor turbine temperature as the energy ofthe power output turbine decreases from the full-load level.

20. A gas turbine engine of the shaft power output type comprising, incombination, a power output turbine having a power output shaft; a gasgenerator including a compressor, combustion apparatus supplied by thecompressor, and a compressor turbine energized by the combustionapparatus connected to drive the compressor, the compressor turbinebeing of sufiicient capacity to drive the compressor at maximum ratedspeed and having excess capacity at lower speeds of the compressor, thegas generator supplying motive fluid to the power output turbine; meansfor controllably supplying fuel to the combustion apparatus, the rate offuel supply determining the output of the gas generator to the poweroutput turbine; and means for transferring mechanical energy from thecompressor turbine to the power output shaft so as to maintaincompressor turbine temperature substantially constant over a wide rangeof energy levels of the power output turbine, the last-recited meansincluding a torque-transmitting coupling of an impositive type betweenthe turbines allowing progressive variation in the relative speeds ofthe two turbines, a transfer control operable to vary progressively thetorque transferred by the coupling, and means responsive to a conditionof the gas generator indicative of compressor turbine excess torquecapacity as limited by compressor turbine temperature and to the torquetransmitted coupled to the transfer control to control the energytransferred so as to maintain substantially full-load compressor turbinetemperature as the energy level of the power outpu turbine decreasesfrom the full-load level.

21. An open-circuit gas turbine engine of the shaft power output typecomprising, in combination, a power output turbine having a power outputshaft; a gas generator including a compressor, combustion apparatussupplied by the compressor, and a compressor turbine energized by thecombustion apparatus connected to drive the compressor, the compressorturbine being of sufficient capacity to drive the compressor at maximumrated speed and having excess capacity at lower speeds of thecompressor, the gas generator supplied motive fluid to the power outputturbine; means for controlled supplying fuel to the combustionapparatus, the rate of fuel supply determining the output of the gasgenerator to the power output turbine; and means for transferringmechanical energy from the compressor turbine to the power output shaftso as to maintain compressor turbine temperature substantially constantover a wide range of energy levels of the power output turbine, thelast-recited means including a torque-transmitting coupling of animpositive type between the turbines allowing progressive variation inthe relative speeds of the two turbines, a transfer control operable tovary progressively the torque transferred by the coupling, and meansresponsive to a condition of the gas generator indicative of compressorturbine excess torque capacity as limited by compresssor turbinetemperature coupled to the transfer control to control the energytransferred so as to maintain substantially full-load compressor turbinetemperature as the energy level of the power output turbine decreasesfrom the full-load level.

22. An open-circuit gas turbine engine of the shaft power output typecomprising, in combination, a power output turbine having a power outputshaft; 21 gas generator including a compressor, combustion apparatussupplied by the compressor, and a compressor turbine energized by thecombustion apparatus connected to drive the compressor, the compressorturbine being of suflicient capacity to drive the compressor at maximumrated speed and having excess capacity at lower speeds of thecompressor, the gas generator supplied motive fluid to the power outputturbine; means for contro-llably supplying fuel to the combustionapparatus, the rate of fuel supply determining the output of the gasgenerator to the power output turbine; and means for transferringmechanical energy from the compressor turbine to the power output shaftso as to maintain compressor turbine temperature substantially constantover a wide range of'energy levels of the power output turbine, thelast-recited means including a torque-transmitting coupling of animpositive type between the turbines allowing progressive variation inthe relative speeds of the two turbines, a transfer control operable tovary progressively the torque transferred by the coupling, and meansresponsive to a condition of the gas generator indicative of compressorturbine excess torque capacity as limited by compressor turbinetemperature and to the torque transmitted coupled to the transfercontrol to control the energy transferred so as to maintainsubstantially full-load compressor turbine temperature as the energylevel of the power output turbine decreases from the full-load level.

References Cited by the Examiner UNITED STATES PATENTS 1,928,301 9/1933Pierson 192--133.2 2,374,510 4/ 1945 Traupel 6049 2,802,334 8/1957Fletcher et al. 6039.16

FOREIGN PATENTS 723,368 2/1955 Great Britain.

231,559 10/ 1945 Switzerland.

413,679 7/1934 Great Britain.

415,788 9/ 1934 Great Britain.

JULIUS E. WEST, Primary Examiner.

1. A GAS TURBINE POWER PLANT COMPRISING, IN COMBINATION, A GAS GENERATORINCLUDING A COMPRESSSOR, COMBUSTION APPARATUS, AND A TURBINE DRIVING THECOMPRESSOR, A LOAD TURBINE GAS-COUPLED TO THE GAS GENERATOR,CONTROLLABLE TORQUE-TRANSMITTING MEANS COUPLING THE TURBINES INCLUDINGMEANS CONTROLLING THE AMOUNT OF TORQUE TRANSMITTED, AND MEANS RESPONSIVETO A CONDITION OF THE GAS GENERATOR INDICATIVE OF TORQUE AVAILABLE FROMTHE GAS GENERATOR AS SHAFT POWER WITHIN ALLOWABLE LIMITS OF GASGENERATOR TURBINE TEMPERATURE CONNECTED TO SAID TORQUE CONTROLLING MEANSTO CONTROL THE TORQUE TRANSMITTED SO AS TO LOAD THE GAS GENERATORTURBINE VARIABLY WITH DECREASE IN ENGINE POWER LEVEL TO MAINTAIN A HIGHGAS GENERATOR TURBINE TEMPERATURE AT LIGHT LOADS.